The present invention relates to a method of forming an article from metal powder by heating and applying fluid pressure against a container of the metal powder.
It has previously been suggested that articles, such as a turbine blade, could be formed of metal powder. When this is to be done, a container having a cavity with a configuration which corresponds to the configuration of the turbine blade is filled with metal powder. The container is then sealed and subjected to hot isostatic pressing in the manner disclosed in U.S. Pat. No. 4,329,175.
It has been suggested, in U.S. Pat. Nos. 4,065,303 and 4,023,966, that a container for a hot isostatic pressing process could be formed by electroplating over a wax pattern. The wax pattern is then removed from the electroplated layer of metal. This results in a container having a cavity with a configuration corresponding to the configuration of the pattern and the article to be formed from metal powder. The container must be thick enough to have sufficient structural strength to be self-supporting during filling of the container with metal powder and during the subsequent compaction of the metal powder at relatively high temperatures and pressures.
Another approach to the forming of a mold for hot isostatic pressing is disclosed in European Patent Application Publication No. 0 090 118. This publication discloses a process wherein a wax pattern is repetitively dipped in a refractory slurry. The layers of refractory material on the pattern are hardened and the wax is removed to leave a mold having an inner surface with a desired configuration. The inner surface of the mold is coated with metal by a chemical vapor deposition process. The mold is then filled with metal powder.
The mold is then "processed in the normal manner" to produce a powder metallurgy part. It is believed this included sealing the mold in a fluid tight container with the mold surrounded by a granular material. Is believed that the fluid tight container is then exposed to fluid pressure to compact the metal powder in the container. During this compaction, it is believed that fluid pressure is applied against the exterior of the container to force it inwardly against the granular material which in turn transmits pressure to the ceramic mold. The force applied against the ceramic mold is transmitted to the metal powder.